What happens after the welcome letter?

You need to go to: http://www.ucas.ac.uk/appenq/index.html (although at the moment it's not working so you'll need to try and use it later)

then click login and when you've logged in, if you click on the choices button it shows you a table with all your universities and the courses (check their right as you can change them if they're wrong up until a certain point)

If it says you have a conditional offer for one of your courses if you click on the course code it will send you to a page giving details of the application and the offer